1. Field of the Invention
The present invention relates to the hydroxylation of phenolic compounds, and, more especially, to the hydroxylation of phenols and phenol ethers with hydrogen peroxide.
2. Description of the Prior Art
Numerous processes for the hydroxylation of phenols are known to this art.
FR-A 2,071,464, in particular, describes a significant industrial process for the hydroxylation of phenols and phenol ethers.
This process entails carrying out the hydroxylation with hydrogen peroxide in the presence of a strong acid. Among these strong acids, sulfuric acid, para-toluenesulfonic acid and perchloric acid are the most widely used.
The hydroxylation of phenol under the conditions described produces a mixture of hydroquinone and pyrocatechol, with a preponderance of the latter, since the hydroquinone/pyrocatechol ratio typically ranges from 0.3 to 0.7.
FR-A 2,266,683 relates to an improvement in the above process, by conducting the hydroxylation in the presence of a ketone. This improves the yield of the reaction with respect to hydroquinone and pyrocatechol. However, in all of the examples, a larger amount of pyrocatechol is produced relative to that of hydroquinone.
The known processes, hence, principally produce pyrocatechol.
Thus, to meet the demand of the commercial market, which fluctuates, need exists for an industrial process that produces hydroquinone as a preponderant final product.